The invention relates to an electric motor having a stator and a rotor which has permanent magnets positioned on a hollow shaft.
In the case of electric motors with permanent magnet excitation, losses mainly occur in the stator. The comparatively lower heat losses of the rotor must nevertheless be dissipated. The problem of rotor heating is particularly serious in the case of electric motors which have a comparatively very long axial length and in which the distances from the center of the rotor to the outside of the end faces of the rotor are comparatively long.
The heat in the rotor reduces the magnetic flux, which results, inter alia, in impairment of the efficiency of the electric motor.
It is known practice to dissipate the losses of the rotor toward the stator via the supporting hollow shaft or via the air gap or to control them by means of an appropriate correspondingly cost-intensive choice of the magnetic material in order to thus reduce the reduction in flux.
Another possible way of dissipating the heat from the rotor is achieved by means of complicated separate ventilation in the rotor.
Another cost-intensive possible way of dissipating the heat from the rotor is to create an axial flow of heat to heat sinks via heat pipes situated in the rotor.